I. Field
The present invention relates generally to communication, and more specifically to techniques for processing signals for transmission via a communication channel.
II. Background
A multi-carrier communication system utilizes multiple carriers for data transmission. These multiple carriers may be obtained with orthogonal frequency division multiplexing (OFDM), discrete multi-tone (DMT), some other multi-carrier modulation schemes, or some other construct. OFDM effectively partitions the overall system bandwidth into multiple (K) orthogonal subbands, which are also commonly called tones, subcarriers, bins, and frequency channels. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data. The data is thus often considered as being transmitted in the frequency domain on a multi-carrier signal. In the following description, the terms “signal” and “waveform” are synonymous and are used interchangeably.
A transmitter in a multi-carrier system typically performs pulse shaping or windowing on a multi-carrier signal prior to transmission via a communication channel. This pulse shaping filters the multi-carrier signal such that its frequency components conform to a spectral mask specified for the system. The pulse shaping ensures that the multi-carrier signal causes negligible interference to other signals that may be transmitted on adjacent frequency bands or radio frequency (RF) channels.
It is sometimes useful to transmit a single-carrier signal in the multi-carrier system. The single-carrier signal may have certain desirable characteristics and may be generated using various techniques, e.g., a spread spectrum technique. The transmitter typically also performs pulse shaping on the single-carrier signal prior to transmission via the communication channel. Unfortunately, the pulse shaping for the single-carrier signal may be very different from the pulse shaping for the multi-carrier signal, as described below. This difference can complicate the design of the transmitter and may pose a problem, e.g., if the system is required to meet different spectral masks.
There is therefore a need in the art for techniques to efficiently process single-carrier and multi-carrier signals for transmission via a communication channel.